1. Field of the Invention
The present invention relates to a main spindle apparatus of a machine tool for working various works and a tool holder clamp unit used therefor.
2. Description of the Related Art
Generally, a main spindle apparatus of a machine tool rotatably supports a main spindle at an inner portion of a main spindle head and mounts a clamp mechanism for clamping a tool holder at a front end portion of the main spindle. A drawing bar for operating to clamp or unclamp the clamp mechanism is contained in a through hole of the main spindle, and a disc spring for biasing the drawing bar in a direction of clamping the tool holder is interposed between a spring receiving member integrally formed at an outer peripheral face of a middle portion of the drawing bar and a stepped portion formed at an inner peripheral face of the through hole of the main spindle in a laminated state. Further, a state of clamping the tool holder by the clamp mechanism is released by moving the drawing bar to a front side in an axial direction against a bias force of the disc spring by a clamp release mechanism provided on the main spindle head side as described in Japanese Patent Unexamined Publication JP-A-1-135403.
However, according to the conventional main spindle apparatus of the machine tool, a front end face of the disc spring is locked by the stepped portion on a side of the main spindle. Therefore, when maintenance, check or repair of failure of a bias mechanism including the clamp mechanism and the disc spring or the like is carried out, the bias mechanism needs to remove from a rear portion of the main spindle and a problem that the operation is very troublesome is occurred.